Recovery of flavoring components from essential oils



a 211 740 RECOVERY OF FLAVORING COMPONENTS FROM ESSENTIAL 011s William L. Stanley, Richmond, and Robert M. Ikeda,

Pasadena, Calif., Sadie H. Vannier, Bethesda, Md., and Lawrence A. Rolle, Altadena, Calif., assignors to the United States of America as represented by the Secretary of Agriculture NO Drawing. Filed May 11, 1961, Ser. No. 109,464

6 Claims. (Cl. 260295) (Granted under Title 35, US. Code (1952), see. 266) A nonexclusive, irrevocable, royalty-free license in the invention herein described, throughout the world for all purposes of the United States Government, with the power to grant sublicenses for such purposes, is hereby granted to the Government of the United States of Amer- This invention relates to and has as its primary object the provision of novel methods for isolating the flavoring principles of an aldehyde or ketone structure from essential oils. Further objects and advantages of the invention will be evident from the following description wherein parts and percentages are by weight, unless otherwise specified.

Many essential oils, including the citrus oils, owe their characteristic aroma and flavor to the presence of aldehydes and ketones. For example, a primary constituent of lemon oil is citral. Usually the essential oils contain other compounds and in many cases these may not contribute to, odor or may even be deleterious. For example, citrus oils contain substantial proportions of terpenes and these are undesirable as, on storage of the essential oil, they become oxidized or undergo other changes with the end result that the oil develops an un- 'pleasant odor resembling that of turpentine. The problem of the instability of citrus oils has been long recognized and much effort has been expended to remedy the situation. Various techniques including distillation and extraction have been advocated to remove the terpenes but none of these provide a practical answer to the problem as they effect deleterious changes to the odor of the oil,'involve cumbersome procedures, or are only partly effective.

By application of the process of the invention, one is enabled to isolate the aldehyde and ketone components in high yield, Without developing off-odors, and by a relatively simple technique.

In applying the process of the invention, the essential oil is first treated to convert its content of aldehydes and ketones into Water-soluble hydrazones. This is accomplished by reacting the essential oil with a hydrazine derivative containing a highly polar group to impart water solubility to the combination of the aldehyde (or ketone) with the hydrazine derivative. Various hydrazine derivatives having such properties may be employed and it is preferred to employ those of the formula ,where X represents a quaternary ammonium radical of the group consisting of wherein R represents a lower alkyl radical, for example, methyl, ethyl, propyl, isopropyl, butyl, etc., and An represents an anion, for example, -Cl, Br, -OSO H,

3,211,740 Patented Oct. 12, 1965 ice OS0 CH or the like. Particularly preferred are the In carrying out the reaction, the hydrazine derivative is used in such amount as to supply at least one mole thereof per mole of carbonyl derivative in the essential oil. An important aspect of the process of the invention is that the reaction is carried out in the presence of a particular type of alcohol solvent, namely, a nonprimary alcohol. (The expression nonprimary alcohol is used herein as designating alcohols having a secondary or tertiary configuration.) In this way, the formation of acetals is prevented. Were acetals to be formed-as would occur if a primary alcohol were used-the yield of isolated aldehydes would be decreased and/or odor changes would result. A preferred solvent is isopropanol but other water-soluble nonprimary alcohols may be employed, for example, butanol-Z, pentanol-2, tertiary butyl alcohol, and the like. The nonprimaryalcohol is generally employed in a volume suflicient to dissolve the essential oil and the reaction products as they are formed. Depending on individual circumstances, one may use anywhere from lto 25 volumes of nonprimary alcohol per volume of essential oil for this purpose. The reaction is carried out at'a temperature of about 50 to C. Generally the reaction is carried out under reflux, in which case the temperature of the reaction is the boiling point of the nonprimary alcohol solvent used. The reaction is complete when the carbonyl compounds have combined with the hydrazine reagent. The reaction may be catalyzed by addition of an acid such as acetic or more preferably by addition of a cation exchange material. The latter is preferred as it does not require neutralization of the reaction mixture and can be readily removed by filtration.

Having prepared the hydrazone formed by reaction of the aldehyde (or ketone) and hydrazine derivative, the reaction mixture is diluted with water and subjected to extraction to remove unreacted components of the essential oil. These would be mainly terpenes in the case of citrus oils. In other cases the unreacted components might include phenols, higher alcohols, esters, hydrocarbons, ethers, higher carboxylic acids, etc. The separation is performed by extracting the reaction mixture with a hydrophobic solvent, for example, hexane, isopentane, petroleum ether, or the like. The reaction product being water soluble remains in the water phase whereas the other components being of a hydrophobic nature are extracted by the solvent. It is of course evident that the resulting extract may be treated by distillation or other techniques to recover the noncarbonyl essential oil components contained therein.

The aqueous phase remaining from the above extraction is then treated to regenerate the aldehyde and ketone components. This is readily achieved by reaction with a molar excess of a water-soluble ketone or aldehyde, for example, formaldehyde, acetaldehyde, glyoxal, beta-ketoglutaric acid, glyoxalic acid, pyruvic acid, acetone, or the like. The reaction is carried out at about -2550 C. and continued until the aldehydes and ketones derived from the essential oil are regenerated from their hydrazone combinations.

Following the regeneration step, the aqueous reaction mixture is extracted with a hydrophobic solvent to separate the regenerated aldehydes and ketones from the water-soluble components of the reaction mixture. Hexane, isopentane, petroleum ether, or other petroleum distillates may be employed as the hydrophobic solvent. It is preferred to use a low-boiling solvent, for example, one having a boiling point not over 60 C. so that in the final step, described below, losses of regenerated aldehydes and ketones of lower boiling point will be minimized. In carrying out the extraction, it is preferred to add a salt to the aqueous reaction mixture in order to decrease solubility of the regenerataed aldehydes and ketones in the water phase. For the purpose sodium chloride is usually used but other water-soluble salts such as sodium sulphate, ammonium sulphate, potassium chloride, and the like may be employed.

In the final step, the extract containing the regenerated aldehydes and ketones dissolved in the hydrophobic solvent is subjected to evaporation, preferably under vacuum, to remove the solvent and leave as the residue the regenerated aldehydes and ketones.

The process of the invention may be applied to any essential oil from which it is desired to isolate the flavoring components having an aldehyde or ketone structure. Thus, for example, the process may be applied to various essential oils, as for example, lemon, orange, lime, grapefruit, bergamot, citronclla, eucalyptus, Verbena, lemongrass, rose, strawberry, rue, linaloe, etc.

The invention is further demonstrated by the following illustrative example- Example Twenty-five ml. (21.2 g.) of lemon oil was added to a 500-ml. flask equipped for heating under reflux and containing ZOO-ml. isopropanol, 0.5 g. of a weakly-acidic cation exchanger of the acrylic resin type (IRC50) in the acid form, and 2 g. of Girard reagent T. The mixture was heated for one hour under reflux, slightly cooled (for convenience in handling) and filtered through coarse filter paper into a separatory funnel, thus to separate the ion exchange resin from the reaction mixture.

The reaction flask was washed with two IO-ml. portions of isopropanol followed by 250-ml. of distilled water and the washings filtered into the separatory funnel. To the mixture in the separatory funnel was added 75-ml. of redistilled hexane. The mixture was shaken vigorously and allowed to stand for 2 hours, after which time the aqueous phase was drawn off and extracted twice with 50- ml. portions of hexane, allowing one hour between extractions for the separation of phases. By this extraction procedure there was obtained an aqueous phase containing isopropanol and the hydrazone derivative formed by reaction of the aldehydes and ketones of the lemon oil with the Girard reagent. The hexane extracts contained the noncarbonyl components of the lemon oil, primarily terpenes.

The aqueous phase from the above-described operation was transferred to a 1-liter glass container and about 80- ml. of 36% aqueous formalin solution was added. The air in the container was displaced with nitrogen and the mixture thoroughly mixed and placed in a constant-temperature bath at 37 C. for 24 hours.

After this period, the container was cooled to bring the solution to about 25 C. and 40 g. of sodium chloride and SO-ml. isopentane were added. The mixture was shaken until the sodium chloride dissolved, then transferred to a separatory funnel. The aqueous phase was separated and extracted with a second 50-ml. portion of isopentane. The isopentane extracts were combined. This composite extract contained the regenerated aldehydes and ketones. To remove isopropanol and other water-soluble components the extract was washed successively with ZOO-ml. of chilled distilled water and 100- ml. of chilled 20% aqueous sodium chloride solution.

The isopentone extract was dried over anhydrous sodium sulfate. Then, isopentane was removed from the extract in a rotary vacuum flask evaporator (bath temperature 30 C., water aspirator vacuum). The residue was the final producta mixture of aldehydes and ketones essentially free from terpenes or other noncarbonyl compounds.

Analyses were made of the total aldehydes present in the original lemon oil and in the product. These determinations indicated that there were 421.4 mg. of carbonyl, calculated as citral, in the lemon oil and 303.2 mg. in the product. The recovery was therefore 71.7%.

It was also determined that the original lemon oil contained 3.4% carbonyl, calculated as citral, whereas the combined hexane extracts applied following reaction with the Girard reagent contained 0.1% carbonyl, calculated as citral. Therefore, about 97% of the carbonyls originally present in the lemon oil were removed by treatment with the Girard reagent.

In a comparative experiment, the process as described above was repeated with the exception that ethanol was substituted for the isopropanol in the first step. It was found that 21% of the aldehydes originally present in the lemon oil were converted into acetals.

Having thus described the invention, what is claimed is:

1. A process for isolating the aldehyde and ketone components from an esesntial oil which comprises reacting the essential oil with a hydrazine derivative of the formula where X is a quarternary ammonium radical of the group consisting of wherein R represents a lower alkyl radical and An represents an anion, in the presence of a water-soluble nonprimary alcohol as a solvent for the reaction, to convert the aldehydes and ketones into water-soluble hydrazone derivatives, diluting the reaction mixture with water, extracting the diluted reaction mixture with a hydrophobic solvent to remove water-insoluble components, reacting the residual aqueous phase with an excess of a member of the group consisting of water-soluble aldehydes and water-soluble ketones to regenerate the aldehydes and ketones derived from the essential oil, extracting the reaction mixture with a hydrophobic solvent to separate the regenerated aldehydes and ketones, and removing solvent from the resulting extract.

2. The process of claim 1 wherein the nonprimary alcohol is isopropyl alcohol.

3. The process of claim 1 wherein the nonprimary alcohol is isopropyl alcohol and the hydrazine derivative 4. The process of claim 1 wherein the nonprimary alcolhol is isopropyl alcohol and the hydrazine derivative ment of carrying out the reaction in isopropyl alcohol as a solvent to minimize formation of acetals.

5 6 6. In the process wherein an essential oil is reacted OTHER REFERENCES Wlth the Compound Dodge, Amer. Chem. J0ur., vol. 12 (1890), pages 553- \N OH2-OONH NH Lederer et al., Bull. Soc. Chim., France, 1949, pages Migrdichian, Organic Synthesis, vol. 1, page 194 to convert the aldehyde and ketone components of the (1957) essential oil into Water-soluble derivatives, the improve- T it lb J O Ch ol. 23, pages 646-7 ment of carrying out the reaction in isopropyl alcohol as (1958),

a solvent to minimize formation of acetals. 10 The Condensed Chemical Dictionary, 4th Ed. (1950),

page 317.

References Cited by the Examiner FOREIGN PATENTS LORRAINE A. WEINBERGER, Primary Examiner.

603,543 8/60 Canada. 15 CHARLES B. PARKER, LEON ZITVER, Examiners. 

1. A PROCESS FOR ISOLATING THE ALDEHYDE AND KETONE COMPONENTS FROM AN ESENTIAL OIL WHICH COMPRISES REACTING THE ESSENTIAL OIL WITH A HYDRAZINE DERIVATIVE OF THE FORMULA 